1. Field of the Invention
The present invention relates to a steering wheel for vehicles, provided with a self-aligning mechanism.
2. Description of the Prior Art
In such a steering wheel 1 in the prior art, as shown in FIG. 1, a deformable member 5 comprising an annular plate 6 and a coupling member 7 with a plurality of arm portions 7a is interposed between a boss 2 and a spoke portion 3 (refer to Japanese U.M. application laid-open No. 9764/1985).
In the steering wheel 1, if the impact force F is applied to a ring portion 4 in the horizontal direction, deformation is produced as follows.
First, the deformable arm portions 7a are plastically deformed from the position I shown in FIG. 1, thereby the surface of the ring portion stands nearly in the vertical direction as shown in the position II of FIG. 2.
Subsequently, if the impact force F is further applied to the whole surface of the ring portion, the cores 3a of the spoke portion are plastically deformed thereby the surface of the ring portion approaches the boss 2 as shown in the position III of FIG. 3.
In this case, the deformation of the deformable arm portions 7a and the cores 3a of the spoke portion contributes to the absorbing of energy of the impact force F. FIG. 4 is a graph showing relation between the load and the stoke at the impact state. The area under the line of the graph represents the energy absorbing amount.
In the steering wheel 1 with such a self-aligning mechanism, rigidity of the deformable member 5 is made lower than that of the cores 3a of the spoke portion.
In such a steering wheel 1 in the prior art, in order to increase the energy absorbing amount at the deformed state, the number of the deformable arm portions 7a or the cores 3a of the spoke portion may be increased, or the thickness of these portions may be increased.
In the cores 3a of the spoke portion, however, since the maximum load at the deformed state must be suppressed within limitation, countermeasure by the number or the thickness of the cores 3a of the spoke portion cannot be taken.
Consequently, countermeasure by the number or the thickness of the deformable arm portions 7a is taken.
However, if the number of the deformable arm portions 7a is increased or the thickness thereof is increased, the initial load at the deformed state of the deformable arm portions 7a is increased and the deformation of the deformable arm portions 7a is not liable to occur thereby the self-aligning mechanism may not act smoothly to the position II shown in FIG. 2. Consequently it is preferable that the deformable arm portions 7a are deformed in the low impact force F applied at the initial state.